Dose mapping of the rectal wall during brachytherapy with an array of scintillation dosimeters
A schematic diagram of the dosimeter used in this study. The scintillator is , coupled to a polymer fiber. The overall diameter is 2.2 mm.
Image of the CCD FOV when the 16 FODs are exposed to the radiation source. A customized software reads the set of pixels uniquely mapped to each FOD. One of the regions assigned to a FOD is shown.
A photograph of the FOD rectal applicator (top). The section taken through the axial plane (bottom) shows the bores through which the FODs are inserted and the three radio-opaque markers used for localization. A section taken through the transverse plane shows the positioning of the bores in the probe.
(a) A schematic of the jig used to calibrate the FOD array (only half is shown). The jig is capable of calibrating up to 24 FODs simultaneously. The FODs are positioned in grooves in Solid Water™ staves (gray) that form a circle, radius 50 mm, centered on the source catheter. The source catheter is kept on the axis of the jig by means of two Perspex wheels (b).
A plot of the frequency distribution of the readings taken with an individual FOD for an exposure time of 1 s over 15 consecutive minutes at a dose rate of 3 mGy/s. (a) Distribution of readings obtained in the dark. The standard deviation is around a mean of . (b) Distribution of the source readings. The standard deviation is about a mean of . At this dose rate, the ratio of the mean source reading to the mean dark reading is 6.4.
Depth dose curve obtained using the CCD system at a source strength of 6.122 Ci (solid circles) compared to values predicted by TG43 (squares). The source was positioned perpendicular to the scintillator axis (therefore, TG43 was calculated at 180°).
Schematic diagrams of the setup used in the simulations of HDR brachytherapy treatments. The upper diagram shows the three dimensional geometry used in treatment planning. The small dots arranged in circles lie on a surface at the locations where dose was calculated using the treatment plan. The FOD scintillators are indicated by large dots. The lower diagram shows the FOD locations in the applicator. Left lateral FODs 2, 3, 4, and 5 are shown, obscuring right lateral FODs 10,11,12, and 13, respectively. The source catheter lies 23 mm from the closest line of FODs and is positioned so that source position 1240 was in line with FOD 1. SUP and INF refer to superior and inferior as is the convention in clinical practice.
(a) The planned dose distribution for the “optimized” plan, calculated by the planning system, presented as a grayscale dose map on the unfolded rectal applicator surface. The individual doses measured by FODs are superimposed on this map for comparison (boxes). (b) Dose profiles along the left lateral, posterior, right lateral and anterior lines through the centers of the FODs. The measured dose readings are shown with crosses at the location of each FOD indicated in the dose map. Experimental uncertainty is indicated by the error bars.
The source position reported by the afterloader (square) and the source position determined from the FOD readings (circle) for the fixed (a) and optimized (b) plans. The error bars in the measured source position were determined from the uncertainty calculated from Eq. (1). The large error bars at the beginning of the treatment are caused by the large source to detector distance (Fig. 7), which would be avoided in a clinical implementation.
(a) Readings obtained from the FOD labeled 2 in the array as the source is driven past the scintillator. The distance from the source to scintillator is 28 mm at the closest approach. The fiber has a helical path within the applicator as shown in Fig. 3 so that the source to fiber distance ranges from 23 to 39 mm. The readings with the source on the fiber side were systematically higher as a result of a small contribution from Cerenkov and fluorescent light generated in the fiber. (b) compares the readings to the source on the fiber side (squares) and non-fiber side (crosses). Note that in (b) the separation between the fiber side and the nonfiber side readings is only apparent at positions greater than 80 mm.
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